1. Field of the Invention
The present invention relates to a high-speed air spindle capable of rotating a spindle at a high speed exceeding 200,000 rpm.
2. Discussion of the Related Art
A machine tool having a high-speed spindle is used in high-precision cutting and machining in die fabrication of, for example, a portable telephone or a camera. The high-speed spindle is available as an air spindle driven by a compressed air, and an electric motor spindle driven by an electric motor. In particular, the air spindle (a) does not operate an electric motor, and is hence free from heat generation source, and is capable of machining at a high speed of about 80,000 rpm stably without being accompanied by thermal distortion, (b) and is small in the number of parts, and small in tool run-out due to imbalance in high-speed rotation, (c) rotates the spindle at a high speed, and is free form change in the depth of cut due to thermal distortion, and is easy in machining in a small diameter, and (d) is small in rotating noise, and has many other features, and it is favorably used in small-diameter machining where cutting and machining of high precision are demanded.
A conventional air spindle is shown, for example, in FIG. 14, in which a spindle 101, having a machining tool 103 for cutting and grinding fixed to the leading end, and an impulse turbine 102 fixed nearly in the center of the spindle, is supported by bearings not shown. In this air spindle 100, the machining tool 103 is mounted on the spindle 101 by, for example as shown in FIG. 15, putting into a collet 104 which is deformed by stress, and tightening a nut 105.
Recently, in small-diameter machining, further, machining at a higher precision and machining in a shorter time are demanded, and it is requested to develop a high-speed spindle capable of rotating at a high speed exceeding 200,000 rpm without any particular axial run-out. A machine tool having such high-speed spindle capable of rotating at super-high speed is capable of machining an extremely small part at high precision, and curtails the machining time and extends the tool life, and brings about outstanding merits.    [Patent document 1] Japanese Patent Application Laid-Open (JP-A) No. 11-13753, claim 1
However, the conventional high-speed spindle rotates at 80,000 rpm at most, and is far from satisfying the above requests. On the other hand, JP-A No. 11-13753 discloses a high-speed spindle, being a spindle incorporating a spindle rotation drive device in its inside, in which the spindle is supported by a pair of rolling elements making planetary motions on the guide surface in the housing at two positions in the axial direction, an air turbine for rotating holders is affixed between two rolling element holders of the holders for holding the rolling elements, and bearing for supporting the holders are provided on the outer circumference of the spindle or on the inner surface of the housing, but stable operation is not obtained at rotating speed exceeding 200,000 rpm even by using a speed-increasing device of high-speed spindle like this.
It is hence an object of the invention to provide a high-speed air spindle extremely small in axial run-out, and capable of rotating the spindle stably at a high speed exceeding 200,000 rpm.